1. Field of the Invention
The present invention relates to a vacuum actuator and more particularly to a vacuum actuator with a fail-safe system.
2. Description of the Prior Art
Vacuum actuators are well known and frequently used as a source of drive for various equipment used in automotive vehicles. One example is illustrated in FIG. 1. Referring to FIG. 1, the known vacuum actuator is provided with a power diaphragm 1 and a control diaphragm 2 having a small diameter as compared to the power diaphragm 1. The power diaphragm 1 and the control diaphragm 2 are mounted within an actuator housing and cooperates with each other to define therebetween a leak or atmospheric chamber 5. The power diaphragm 1 defines on the opposite side of the atmospheric chamber 5 a power diaphragm or servo chamber 3, while the control diaphragm 2 defines on the opposite side of the atmospheric chamber 5 a control diaphragm chamber 4.
Secured to the power diaphragm 1 is a push rod 6 which is supported by bearings 7 and 8 and extends through an air seal 9. The push rod 6 is formed with a power vacuum controlling passage 10 which extends inwardly from an open end 10a thereof communicating with the leak chamber 5 and terminating in a radial hole communicating with the power diaphragm chamber 3. Mounted within the power diaphragm chamber 3 is a power diaphragm spring 11 which biases the power diaphragm 1 to the left as viewed in FIG. 1 and in turn the push rod 11 toward a retracted position thereof. Provided for the power diaphragm chamber 3 is a connector 12 which is coupled with a power vacuum conveying hose 13 leading from a source of power vacuum (for example, an intake manifold of an internal combustion engine). Provided for the leak chamber 5 is an atmospheric air admission or vacuum leaking connector 14 which is coupled with an atmospheric air conveying hose 15 leading from a source of atmosphere such as an air cleaner opening to the ambient atmosphere.
Fixed to the control diaphragm 2 is a valve element or valve seat 16. This valve seat 16 is arranged in face-to-face relationship with the open end 10a of the push rod 6. Mounted within the control diaphragm chamber 4 is a control diaphragm spring 17 which biases the control diaphragm 2 to the right as viewed in FIG. 1 and in turn the valve seat 16 toward the open end 10a of the push rod 6. Provided for the control diaphragm 4 is a connector 18 which is coupled with a control vacuum conveying hose 19 leading from a source of control vacuum.
In operation, a control vacuum which may be obtained, for example, by pressure regulation on duty control is admitted to the control diaphragm 4. This causes the control diaphragm 2 to move against the spring 17. With this movement of the control diaphragm 2, a clearance space between the valve seat 16 and the open end 10a of the power vacuum controlling passage 10 is adjusted, adjusting the flow of air from the leak chamber into the power diaphragm chamber 3, thus controlling the power vacuum within the power diaphragm chamber 3. The power diaphragm 1 moves against the spring 11 in response to the power vacuum therein, thus controlling the projected position of the push rod 6.
According to this known vacuum actuator, when the vacuum within the control diaphragm chamber 4 disappears, the valve seat 16 movable with the control diaphragm 2 blocks the power vacuum controlling passage 10, preventing a reduction in the vacuum within the power diaphragm chamber 3, thus allowing the push rod 6 to move with the power diaphragm 2 up to its full stroke projected position. Therefore, a problem presented by this known vacuum actuator is that the push rod 6 would move to its full stroked position and thus malfunction toward a danger side should the vacuum within the control diaphragm chamber 4 disappear owing to breakage of the actuator itself, removal of the control vacuum conveying hose 19, or breakage thereof.